1. Field of the Invention
The present invention relates to a mask to be used when machining a material and a method of fabricating the mask, and further relates to a method of machining a material.
2. Description of a Related Art
Conventionally, as a machining method of a hard and brittle material such as glass or ceramic or a method of micro machining a semiconductor, the sandblasting method and the dry or wet etching method are known. The sandblasting method is a machining method of performing drilling and polishing a workpiece by blasting a polishing material (abrasive grain) at high pressure (for example, 0.3 MPa to 0.4 MPa) from a nozzle to spray the material on the workpiece. In the sandblasting method, a nozzle having a diameter about 0.5 mm to 5 mm is generally used, and, further by using a mask, a micro pattern can be formed on the hard and brittle material. Such sandblasting method is used in the fields such as the manufacture of a plasma display panel, the manufacture of an ultrasonic transducer array, and MEMS (micro electromechanical system) related devices. Further, the plasma etching method as one of the dry etching methods is a technique for etching a workpiece by making a reactive gas into a plasma state under low vacuum pressure, and mainly used for micromachining a semiconductor.
In the sandblasting method, a member having elasticity such as a dry-film resist is used as a mask. The reason is as follows. Since not only the target of machining but also the mask is damaged by the sprayed abrasive grain, it is necessary to absorb the shock by the abrasive grain. Further, in order to endure the reduction of the mask thickness, the mask is made to have a certain degree of thickness.
Generally, in the case where a hard material is machined or a target of machining is deeply drilled by the sandblasting method, abrasive grain is blasted for a long time. However, the longer, the blasting time of abrasive grain, the greater the damage to the mask becomes. Especially, since the edge portion in the mask peripheral part is damaged greatly, the mask peripheral part recedes and the mask shape cannot be maintained. On this account, the formed pattern becomes tapered, and thus, there has been a problem that formation of a precise pattern with a high aspect ratio (drilling depth: pattern width) is difficult by the sandblasting method.
In order to reduce the mask damage due to abrasive grain, it is conceivable that a hard member such as a metal is used as a mask. However, if a member such as a metal is used, the shock by the abrasive grain cannot be absorbed, and the durability of the mask becomes degraded instead. Further, in order to make the mask usable for a long time even if the mask is damaged, it is conceivable that the thickness of the mask is made thicker. However, if the mask becomes thicker, the capability to reliably shield the target of machining from abrasive grain is degraded, and therefore, the accuracy of the pattern formation becomes lower.
The following three documents, Japanese Patent Application Publication JP-A-5-205636, JP-A-6-243789, and JP-A-6-251702 disclose that the sandblasting method is used when a plasma display substrate is manufactured. From among the three documents, the first document JP-A-5-205636 discloses in FIG. 3 a metal mask formed by providing an adhesive layer 12 on the back side of a metal thin plate 11 and a protective layer 13 on the front side thereof. The adhesive layer 12 brings the metal mask into close contact with the upper surface of a barrier 2 (FIG. 1 of the first document) and absorbs the rebound force of an abrasive at the time of sandblasting treatment. The protective layer 13 absorbs the shock of the abrasive at the time of sandblasting treatment and prevents the metal thin plate 11, especially its edge portion from wear, heat generation, and deformation. Further, the first document also discloses in FIG. 4 a metal mask having greater effect of absorbing the rebound force of an abrasive at the time of sandblasting treatment by further providing a cushion layer 14 consisting of a dry film between the metal thin plate 11 and the adhesive layer 12 in the above-mentioned metal mask.
Thus, by using a composite mask in combination of a soft material and a hard material, the durability of the mask can be improved. However, such composite mask is for forming a “hollowing-out pattern” to be used when fabricating a fluorescent material pattern. That is, there is a problem that mask for forming an isolated pattern, which is a reversal pattern of the “hollowing-out pattern”, cannot be fabricated by the methods disclosed in the above-mentioned documents.